As computers including mobile devices, handheld devices and related technology such as displays have evolved, human input mechanisms have similarly advanced. Natural user interfaces such as based upon speech recognition, head and skeletal tracking and gesture detection are becoming more widespread to supplement, or in some cases replace, keyboard, pointing device (mouse or stylus) and/or recognized symbol/handwriting input. Eye gaze detection is another natural user interface technology.
One type of eye tracking technology is referred to as cross-ratio (CR) based eye-tracking. This technology exploits the invariance of a plane projectivity to enable remote gaze estimation of a subject using a single camera in an uncalibrated setup. In general, infrared light is projected towards a user, with corneal reflections from the user's eye (glints) sensed by the camera and processed to track the gaze.